1. Field of Invention
This invention relates to the manufacture of flexible coated fabrics with high barrier properties.
2. Description of Related Art
The attachment of polymeric coatings to flexible webs (e.g. fabrics) to provide a flexible composite with barrier properties, for example waterproofness, is well known. Existing methods typically employed to produce such composites from flexible webs include the lamination of pre-formed films (laminating), such as taught in, e.g., U.S. Pat. Nos. 5,709,766 and 5,902,753; the direct application of liquid coating compositions followed by drying and/or curing (direct coating), such as taught in, e.g., U.S. Pat. Nos. 5,902,753 and 6,734,123; and the application of liquid coating compositions to a temporary carrier having release properties, followed by drying and/or curing before being transferred from the carrier and adhered to the substrate web (transfer coating), such as taught in, e.g., U.S. Pat. No. 4,233,358. A fourth method related to direct coating, involves the direct application of molten polymer to a flexible web, followed simply by cooling (extrusion coating). Each method has its inherent advantages and disadvantages, summarized in Table 1 below.
TABLE 1Composite Fabric Manufacturing MethodsMethodAdvantagesDisadvantagesLaminationEconomicalNarrow formulating latitudeLow emission processingLeak-proof via thick ormultilayer constructionDirectModerately economicalNot well suited to stretch, orCoatingWide formulating latitudebulky fabrics Difficult toattain leakproofnessTransferWide formulating latitudeExpensiveCoatingSuitable for high stretchRequires multi-station coatingand bulky fabricsto attain leakproofnessExtrusionEconomicalNarrow formulating latitudeCoatingLow emission processingLeak-proof via thick ormultilayer construction
Dartex Coatings, Inc., a well-established coater and laminator of textiles which is located in Slatersville, R.I., supplies polyurethane (PU) coated liner fabric to the sewer pipe rehabilitation market where its customers fashion it into tubular form, saturate its fabric side with a curable resin, line a damaged host pipe with the saturated fabric and then allow it to cure, thereby repairing the host pipe and restoring service through the host pipe in a manner which is more economical and less disruptive than the alternative method of digging a trench and replacing the pipe section. This useful technology is commonly referred to as “trenchless” cured-in-place pipe (CIPP) rehabilitation.
The liner fabric requires a modest amount of liquid barrier properties along with good resin saturation and resin holding capability on its uncoated surface. This combination of properties is easily obtained using Dartex's current transfer coating line where a temporary, release paper carrier is coated with a PU solution, dried, then overcoated in-line with an adhesive solution, into which a high pile knit fabric is introduced. Finally, the adhesive layer is dried and upon cooling the composite fabric is stripped free of the paper carrier, yielding the coated fabric. Produced in this manner, and by virtue of the following balance of properties, Dartex's liner fabrics have enjoyed success in the gravity-driven, sewer pipe rehabilitation market:                Good resin saturation receptivity combined with resin holding capacity and control        Excellent controlled stretch and flexibility        Good overall durability, especially towards the liner installation process while resin-saturated        Decent barrier properties        
A relatively recent goal of Dartex is to expand its market into liners suitable for pipes that transport water or other liquids under relatively high pressure, including those transporting potable water. In order to satisfy this more demanding application, these pressure pipe liners would need to ensure a much higher degree of liquid barrier properties (e.g., waterproofness) and robustness, not to mention the process latitude allowing for barrier layer composition and thickness variability to meet each pipe rehabilitation situation.
Achieving this goal on a transfer coating line having only two coating stations poses a difficult challenge. In fact, since the “barrier” layer would have to be cast from solution at the first, single coating head, there would be severe limits imposed on the maximum thickness attainable, not to mention that it would be nearly impossible to guarantee substantially leakproof quality when depending upon just one layer. (It should be noted that the second, adhesive layer in practice does not contribute significantly to barrier properties, presumably since the introduced fabric layer protrudes into and through it while wet.)
Accordingly, there exists a desire to devise a transfer-coating process that will enable the production of composite fabrics having barrier layers of variable composition and thicknesses with substantially leakproof characteristics. It is further desired that such composite fabrics be sufficient flexible for use in CIPP repair.
All references cited herein are incorporated herein by reference in their entireties.